Raining cats and dogs.
She had a cow. She was upset.
A little birdy told me the secret.
He’s such a scaredy cat.
It’s a dog-eat-dog world. situation in which people will do anything to be successful, even if what they do harms other people
There's something fishy going on here. Something seeming dishonest or false.
I have bigger/other fish to fry. To have something more important to do
He drinks like a fish. He drinks a lot of alcohol.
I was like a fish out of water . to feel awkward because you are in an situation which you have not experienced before or because you are very different from the people around you.
He was fishing in my pocket for something to steal.
If someone tells you to let sleeping dogs lie, they are asking you not to interfere with a situation so that it does not become a problem.
If you help a lame dog over stile, you help someone who is in difficulty or trouble. "You can trust him - he always helps a lame dog over a stile."